Vulcanization of rubber



" nesium.

VULCANIZATION F RUBBER Russell T. Dean, Stamford, Conn., assignor toAmerican Cyanamid Company,

New York,

N. Y., a corporation of Maine No Drawing. Application December 31, 1941,Serial No. 425,234

12 Claims.

wherein R may be an alkyl, aralkyl or aryl group which may be the sameor different. The alkyl group may be acyclic or cyclic. These radicalsmay contain substituents which do not change the essential character ofthe compound such as halogen atoms, nitro groups, hydroxy groups, etc. Ris an alkylene group which separates the oxygen atom from the nitrogenatom by at least two carbon atoms. This group may contain substituentsof the kind described above in respect to f the groups represented by Ras well as aryl and substituted aryl radicals. R may represent like orunlike alkylene radicals. M is a salt-forming group or an organicradical and n is the valence of M.

In the above formula, M may be a heavy metal such as zinc, cadmium andlead, an. alkali metal such as sodium and potassium or an alkaliney'arth metal such as calcium, barium and mag- It may be the ammoniumradical or a salt forming group derived from the alkyl, aralkyl, aryland heterocyclic amines, a guanidinium group derived from guanidine,diphenyl guanidine, diortho-tolyl guanidine, a pyridinium group, etc.

The dithiocarbamic acid derivatives constituting the vulcanizationaccelerators of the invention may be prepared by methods known to theart for the preparation of similar derivatives of similar dithiocarbamicacids. The various dithiocarbamic acids may be prepared in the form oftheir sodium salts by reaction-of carbon disulflde, a secondary amineand sodium hydroxide in the presence of a suitable solvent. By employingammonium hydroxide in place of the sodium by- Methyl amine droxide inthis reaction, the corresponding ammonium dithiocarbamates may beprepared. By employing the sodium dithiocarbamate from the abovereaction as one component of a double decomposition reaction, variousother metal salts and organic nitrogen base salts of the dithiocarbamicacid may be obtained by the addition to a solution of the sodiumdithiocarbamate of a salt of the desired metal or organic nitrogen base,e. g., the chloride orthe hydrochloride respectively. As will beunderstood by those skilled in the art, the solvent employed in thisdouble decomposition reaction should be preferably so selected that itis a solvent for on y one of the reaction products, thus providing forselective separation of th same. Where the salt prepared is thedithiocarbamic acid salt of an organic nitrogen base, the solutioncontaining the same may be concentrated under reduced pressure and theresidue dried in vacuo to obtain the salt in its 1 anhydrous form.

Any of the various salt-forming organic nitrogen bases can be employedin the foregoing man- Aniline N-ethyl aniline N-cyclohexyl anilineDimethyl amine Trimethyl amine The parent secondary amine salts of thedithiocarbamic acids are preferably prepared by reaction in known mannerbetween one mol of carbon dis'ulfide and two mols of the secondaryamine. water or other suitable solvent being employed in the reaction.

The thiuram disulfides may be conveniently prepared by the oxidation ofthe sodium dithiocarbamate in aqueous solution with hydrogen peroxidecontaining sufficient sulfuric acid to neutralize the sodium hydroxideformed. The thiuram monosulfides may be prepared from the thiuramdisulfides by desulfurizing the thiuram disulfide in alcoholic solutionwith a molecular equivalent of potassium cyanide.

added and the mixture cooled to 17 C.

The esters or-other organic derivatives of the dithiocarbamic acidsmaybe prepared by reaction of the sodium dithiocarbamate with a reactivehalogen-containing compound such as.

ROR'

NH ROR' I wherein R and R' represent radicals identical with thosedescribed in the above general formula. Examples of the secondary aminesare.

Bis (2-methoxy ethyl) amine Bis (2-ethoxy-n-butyl) amine Bis(2-ethoxy-n-amyl) amine Bis (Z-ethoxy n-hexyl) amine Bis(2-ethoxy-(3'-methyl amyD) amine Bis (2-ethoxy-2-benzyl ethyl) amine Bis(2-ethoxy-2-phenylethy1) amine Bis (2-phenoxy ethyl) amine L Bis(2-p-naphthoxy ethyl) amine Bis (2-p-methylphenoxy ethyl) amine Bis(3-methoxy-n-propyl) amine Bis (3-ethoxy n-propyl) amine Bis(3-isopropoxy-n-propyl) amine Bis (3-n-butoxy-n-propyl) amine Bis (3(2'-ethylhexoxy)n-propyl) amine Bis (3-octadecoxy-n-propyl) amine .Bis(S-phenoxy-n-propyl) amine Bis (3-cyclohexoxy-n-propyl) amine.

Bis (4-phenoxy-n-but'yl) amine Bis (3-(2'-etl 1oxyethoxy) -n-propyl)amine Bis (3- (2'-ethylhexoxy)-isobutyl) amine The preparation ofvarious derivatives of the dithiocarbamic acids is illustrated by thefollow:

ing examples, EXAMPLE 1 5 Zmc BIS (3-E'rr-roxY PROPYL) DI'I'HIOCARBAMATE840 grams of 95% sodium hydroxide mols) were dissolved in 16 liters ofwater and cooled to 17 C. by the addition of cracked ice. 3780 grams ofhis (3-ethoxy propyl) amine (20 mols) were 1520 grams of carbondisulfide (20 mols) were then added slowly with good stirring and thereaction thiocarbamate, was a fine white powder with a melting point of66-69 C. The analysis for zinc gave a value of 11.37% as compared to atheoretical value of 10.96%.

ExAMPLn2 Sonruu BIS (3-Errroxr Paorxr.) Drrmoc mamna 66 grams of his(3-ethoxy propyl) amine and 28 grams of 50% sodium hydroxide weredissolved in 80 cc. of- -water and cooled to 5C. 26.5 grams of carbondisulfide were added slowly with good stirring and the temperature ofthe reaction mixture kept below C. "When the carbon' disulfide was nolonger perceptible the solution was clarified. A solution of sodium bis(3-ethoxy propyl) dithiocarbamate of 50% concentration was thusobtained. The anhydrous form of the sodium salt may be obtained byconcentrating the solution under reduced pressure and drying the residuein vacuo over concentrated sulfuric acid. The anhydrous product is aviscous balsam.

EXAMPLE 3 B15 (B-Ernoxy mm). Amrormm B15 (3- ErnoxY PROPYL) Drrmoclmsmrn84.grams of bis (3.-ethoxy propyl) amine were dissolved in 100 oddwaterand cooled to 5 C. 17 grams of carbon disulfide were added in smallportions and the mixture well-stirred until clear, the temperature ofthe reaction mixture being kept below 25 C." The product was a 50%solution of the amine salt. The anhydrous form of the amine salt may beobtained by concentrating the solution under reduced pressure and dryingthe residue in vacuo over concentrated sulfuric acid. The anhydrousproduct. is an orange balsam.

EXAMPLE 4 Tarn'axrs (3-Mamoxv PaorYr.) Tnroniim DISULFIDE A solution of81 grams of his (3-methoxy propyl) amine in 200 cc. of water was cooledto 10. C. and 38 grams of carbon disulfide gradually added thereto. Acold solution of 20 grainsv of sodium hydroxide in 100 cc. of water wasthen added with good stirring. The temperature of the reaction mixturewas kept below 10 C. After the liquid mixture became clear (one hour)the volume was increased to one liter by the addition of cold water andthe resulting solution clarified.

mixture kept below 20 C. When the unreacted carbon disulfide was nolonger perceptible, the solution containing the sodium dithiocarbamatewas clarified and then cooled to 10 C. by the addition of cracked ice.The zinc salt was formed by slowly adding to the solution of the sodiumsalt, with good stirring, 1435 grams-of 95% zinc chloride (10 mols) ineight liters of cold water. The zin'c'salt precipitated immediately andcrystallization was aided by seeding with a previously prepared sampleof the same material. The addition took about one half hour followingwhich the mixture'was stirred for an additional half hour and thenfiltered. The product was thoroughly washed with water, reslurried inten liters of water, filtered and again washed with water, and dried for24 hours at 40 C. The product, zinc bis (3"-ethoxy propyl) di- Tothissolution was added a cold mixture of 29 grams of 30% hydrogen peroxide,109 grams of 22% sulfuric acid and 300 cc. of water over a period or onehour. The product separated as a light yellow oil which was washed wellwith waterand desiccated in vacuo over'concentrated sulfuric acid.

The product analyzed nitrogen 5.94% and sulful 26.75% as compared withthe theoretical values of 5.93% and 27.11% respectively.

EXAIVIPLE 5 TETRAKIS (B-METHOXY PROPYL) THIURAM MONO- SULFIDE A mixtm-eof 47 grams of tetrakis (3-methoxy propyl) thiuram disulfide, 6.5 gramsof potassium cyanide and 200 cc. of'ethyl alcohol was stirred at 45-50C. for 2 /2 hours. The reaction mixture was clarified and evaporated tohalf volum under reduced pressure. At this. point a solid believed to bepotassium thiocyanate was filtered oil and the evaporation completed..The

resulting thick liquid was well-washed with water and desiccated invacuo over concentrated sulfuric acid. The product was obtained as adark red oil which was soluble in alcohol and ether but insoluble inwater.

The product analyzed 6.30% nitrogen and 21.40% sulfur as compared to thetheoretical of 6.36% and 21.82% respectively.

EXAMPLE 6 2.4 Drmraornam Brs (3-MarnoxY Paorrr.) Drrmocanam'rn Asolution of sodium bis (3-methoxy propyl) dithiocarbamate was preparedby the interaction of 16 grams of bis (3-methoxy propyl) amine, 8 gramsof carbon disulfide and 4 grams of sodium hydroxide in 275 cc. ofethanol at 25 q. It was clarified and heated to 50 C. A solution of 2,4

dinitrochlorbenzene. in 200 cc. of ethanol was added dropwise withstirring over-a period of V2 hour, the temperature being maintained at45- 55 C. After the reaction was complete, the solid which was believedto be sodium chloride was filtered off and the mother liquor evaporatedto small volume under reduced pressure. The oil -which separated wastaken up in ether, and the ether solution washed with water and driedover anhydrous sodium sulphate. Removal of the ether in the usual mannergave the product in the form of a dark, viscous oil.

In general, the vulcanization accelerators of the invention have goodsolubility in rubber and for the most part are accelerators of the ultratype and therefore suitable for the vulcanization of latex.

The activity of the compounds as accelerators for the vulcanization ofrubber was tested as follows.

Dry rubber mixes were prepared in accordance with the formula,parts'bein'g by weight.

Smoked sheets 100 Stearic d I 1 Zinc oxide 5 Sulphur 2.5 Accelerator 0.5

The samples were vulcanizedin the usual manner. In the following table,A represents zinc bis (S-methoxy propyl) dithiocarbamate and Brepresentszinc bis (3-ethoxy propyl) dithiocarbamate.

TABLE I M dul 'r il us n cc l q I at 500% lbs/sq. in.

Temperature Tim (1, Min. 120 l, 075 225 105 3 660 4,575 D f 20 900 4, 1105 475 4 0 In a similar manner, tetrakis (3-methoxy propyl) thiuramdisulfide and tetrakis (3-methoxy propyl) thiuram monosulfide v reemployed as accelerators in a dry rubber stock of the following formulain which parts are by weight.

Smoked shee 100 Stearic acid 1 Zine oxide 5 Sulfur 2.5 Accelerator 0.25

After vulcanization of the stocks in the usual manner, the vulcanizateswere tested for Shore hardness with the results given in the followingtable, in which E denotes tetrakis (3-methoxy propyl) thiuram disulfldeand F denotes tetrakis -(3-methoxy propyl) thiuram monosulfide.

5 Press cure at 121 0.

Shore hardness Time of cure in minutes Accelerator Accelerator No cureNo cure 41 44 47 47 49 49 Latex sheets were prepared from the followingformula, parts being by weight. Latex (62% solids) -a 162 Casein (10%)1o gu'wettin'g agent i 1 Zinc oxide dispersion (50%) 2 Sulfur dispersion(50%) 3 Water 32 Accelerator See Table II The latex sheets were curedfor 25 minutes at 100 in a current of hot air. In the following table ofresults, the accelerators denoted by A and B are zinc bis (3-methoxypropyl). and zinc bis (3-ethoxy' propyl) dithiocarbamate respectively, 0represents sodium bis (3-methoxy propyl). dithiocarbamate and Drepresents sodium bis (3-ethoxy propyl) dithlocarbamate.

TABLE II Modulus Tensile Accelerator Parts (590%) Strength 0.75 5004,270- B 0.75 580 4. 200 c aqueous solution). 1.50 1.170 4.355 D (50%aqueous solution) l. 50 l, 480 4, 520

Further illustrative of the invention are the following dithiocarbamateswhich were also tested and found to be accelerators of the vulcanizationof rubber.

The accelerators of the present invention may be employed in accordancewith known procedures for the vulcanization of rubber and the amountsthereof may be varied to meet individual requirements, as will beunderstood by those skilled in the art. The accelerators may also beused in conjunction with known accelerators where special results aredesired. While, in general, the

bis (3-meth0xy propyl) dithiocaruse of activators with the acceleratorsof the ill--v vention is not necessary, the usual activators,

4 I 2,340,650 e. g. diphenylguanidine and di-orthotolyl c'uanieratorwhich is a dithiocarbamic acid derivative dine, may be employed foractivation of those having the formula members or the class which are orlow activity. S

The term "rubber appearing in the specification and the claims is usedin the generic sense N C S N and is intended. to include not onlynatural rubnon bers but bers.

The accelerators oi the present application are claimed as new chemicalcompounds in my copending application Serial No. 424,921, filed December30, 1941. The-amine salts as rubber vulalso sulfur-vulcanizablesynthetic rub- .canization accelerators are more specifically claimed incompanion application Serial No.

- 425,236, filed December 31, 1941.

While I have described certain specific embodiments of my invention, itis to be understood that the invention i not to be limited thereto butis to be restricted solely by the scope of the appended claims construedas broadly as is permissible in view of the prior art.

I claim: r

1. A process of treating rubber which comprises vulcanizingit in thepresence -of an accelerator which is a dithiocarbamic acid derivativehaving the formula prises vulcanizing a rubber mix containing avulcanizing agent'and zinc bis (3-ethoxy propyl) dithiocarbamate.

4.- A process of treating rubber which comprises vulcanizing it in thepresence of an accelerator which is .a dithiocarbamic acid derivativehaving the formula v wherein R is an alkyl radical and R is an alkyleneradical which separates the oxygen atom from the nitrogen atom by atleast two carbon atoms and M is an alkali metal.

-5. A process of treating rubber which comprises vulcanizing it in thepresence of an accelwherein R is an alkvl radical and R is an alkyleneradical which separates the oxygen atom from the nitrogen atom by atleast two carbon J atoms.

6. A process of treating rubberwhich comprises vulcanizing a rubber mixcontaining a vulcanizing agent and sodium bis (3-ethoxy propyl)dithiocarbamate.

7.'A rubber product which has been vulcanized in the presence of adithiocarbamic acid derivative having the formula wherein R is an alkylradical, R is an alkylene radical which separates the oxygen atomfromthe'nitrogen atom by at least two carbon atoms, M is a heavy metal,and n is the valence of M.

8. A rubber product which has been vulcanized in-the presence of a zincbis (2-methoxy ethyl) dithiocarbamate.

- 9. A rubber product which has been vulcanized in the presence of zincbis (3-ethoxy propyl) dithiocarbamate.

10. A rubber product which has been vulcanized in the presence of adithiocarbamic acid derivative having the formula from the nitrogen atomby at least two carbon atoms and M is an alkali metal.

11. A rubber product which has been vulcanized in the presence of adithiocarbamic acid derivative having the formula wherein R is an alkylradical and R. is an alkyl-' ene radical which separates the oxygen atomfrom the nitrogen atom by atleast two carbon atoms.

12. A rubber product which has been vulcanized in the presence of sodiumbis (3-ethoxy propyl) dithiocarbamate.

RUSSELL T. DEAN.

